In a fuel cell system that generates electricity with supplies of hydrogen and oxygen to fuel cells, various techniques of detecting a leakage of hydrogen supplied to anodes of the fuel cells have been proposed to enhance the safety of the fuel cell system.
One proposed technique of leakage detection disclosed in JP-A-2003-148252 estimates a quantity of pressure decrease in a hydrogen supply flow path from a total quantity of hydrogen as the sum of the quantity of hydrogen consumed for power generation by the fuel cells and the quantity of unconsumed hydrogen discharged from the fuel cells. The leakage detection technique then compares the estimated quantity of pressure decrease with an actual quantity of pressure decrease measured by a pressure sensor and detects the occurrence of a hydrogen leakage in the hydrogen supply flow path based on the result of the comparison.
Other known techniques of detecting a gas leakage are disclosed in, for example, JP-A-11-108730, JP-A-2003-308868, and JP-A-2003-308866.
In the general structure of the fuel cell system, a pressure regulator is provided in the hydrogen supply flow path to reduce the pressure of high-pressure hydrogen supplied from a hydrogen tank. During power generation by the fuel cells, the pressure level in the upstream of the pressure regulator is different from the pressure level in the downstream of the pressure regulator. In the occurrence of a hydrogen leakage at a specific position, the pressure sensor may have difficulty in measuring the quantity of pressure decrease of hydrogen. For example, the pressure sensor is provided in the upstream of the pressure regulator, and a hydrogen leakage occurs in the downstream of the pressure regulator. In this case, the pressure regulator interferes with transmission of a pressure variation accompanied with the hydrogen leakage occurring in the downstream of the pressure regulator. The pressure sensor located in the upstream of the pressure regulator is thus unable to accurately detect the pressure variation. The pressure variation in the downstream of the pressure regulator is transmitted to the upstream only after the continuous hydrogen leakage in the downstream of the pressure regulator decreases the pressure to or below a predetermined level to open the pressure regulator.